1. Field Of The Invention
This invention relates generally to information reproducing apparatus and, more particularly, is directed to an apparatus suitable for reproducing digital data recorded on a magnetic recording medium.
2. DESCRIPTION OF THE PRIOR ART
It is known to employ an 8-mm format video tape recorder (VTR) as an apparatus for the play back or reproducing of digital data recorded on a magnetic tape. In such 8-mm format VTR, an FM audio signal is interposed between the frequency band of a FM luminance signal and the frequency band of a low-frequency converted chrominance signal, and the resulting combined signal which is hereinafter simply referred to as a video signal is recorded in video track portions TR.sub.VD constituting the main portions of successive slant record tracks TRA and TRB which are disposed alternately on a magnetic tape 1, as shown on FIG. 7. In order to record and/or reproduce audio signals of higher quality, in the 8-mm format VTR, the audio signals are PCM-encoded, time-base compressed and recorded in so-called overscan or audio track portions TR.sub.AD situated at one of the end portions of the slant tracks TRA and TRB. A particular type of modulation used to record the time-compressed, PCM-encoded audio signals is bi-phase-mark modulation, for example, as described in detail in U.S. Pat. No. 4,551,771, issued Nov. 5, 1985, and having a common assignee herewith. As shown in FIG. 8A, in bi-phase-mark modulation, frequency signals S.sub.1 and S.sub.2 having frequencies f.sub.1, for example, of 2.9 MHz, and f.sub.2, for example, of 5.8 MHz, are recorded as digital data on the magnetic tape while maintaining a phase relationship in which their zero cross points coincide with each other. For example, when a PCM audio signal is at logic "L", the frequency signal S.sub.1 having the low frequency f.sub.1 is recorded, whereas, when the PCM audio signal is at logic "H", the frequency signal S.sub.2 having the high frequency f.sub.2 is recorded on the magnetic tape.
When an audio signal recorded in an audio track portion TR.sub.AD is reproduced or played back, the zero cross points of the picked-up frequency signal S.sub.1 or S.sub.2 are detected, as shown in FIG. 8B. In response to such detection, for example, a sampling pulse oscillator with a phase locked loop (PLL) arrangement is made to oscillate and thereby provide output pulses PLL.sub.0 which are phase shifted 45.degree. from the frequency signal S.sub.1 having the low frequency f.sub.1, or phase shifted 90.degree. from the frequency signal S.sub.2 having the high frequency f.sub.2. Those of the output pulses PLL.sub.0 generated at the phase angles of 35.degree., 135.degree., 225.degree. and 315.degree. of the frequency signal S.sub.1 are used as sampling pulses P.sub.S (FIG. 8C) for sampling the reproduced data. When every other two of the resulting sampled values are positive, it is determined that the respective reproduced data is at the logic level "L". Further, those of the output pulses PLL.sub.0 generated at the 90.degree. and 270.degree. phase angles of the frequency signal S.sub.2 are also used as sampling pulses P.sub.S for sampling the reproduced data and, when every other of these sampled values are positive, it is determined therefrom that the respective reproduced data is at the logic level "H". The reproducing of bi-phase-mark modulated data is further described in U.S. Pat. No. 4,542,418, issued Sept. 17, 1985, and having a common assignee herewith. Furthermore, an audio PCM signal reproducing circuit in which the equalizing function is automatically changed-over in response to the characteristic of the recorded tape is disclosed in U.S. Pat. No. 4,841,385, issued June 20, 1989, and corresponding to EPO laid-open Publication No. 0264228, which also has a common assignee herewith.
As shown more specifically in FIG. 9, the video signal S.sub.VD recorded in the video track portion TR.sub.VD of each of the tracks TRA and TRB is known to include an FM luminance signal, for example, as indicated at S1V.sub.N, a low frequency or down-converted chrominance signal S3V, and an FM audio signal, for example, as indicated at S2V.sub.M interposed between the frequency bands of the signals S1V.sub.N and S3V. An automatic track follower (ATF) signal S.sub.ATF is superposed on the signal S.sub.VD for recording therewith in each video track portion TR.sub.VD. The same rotary magnetic head used for recording the signal S.sub.VD in each video track portion TR.sub.VD is also used for recording the PCM audio signal S.sub.ADNR in the audio signal portion TR.sub.AD of the respective track. The frequency spectrum of the PCM audio signal S.sub.ADNR is shown on FIG. 9 to have a peak value at a frequency which substantially coincides with the center frequency of the FM luminance signal S1V.sub.N. Further, the PCM audio signal S.sub.ADNR has a frequency characteristic in which the signal level nears zero in the high and low frequency ranges of the signal S.sub.VD. By reason of the foregoing, the same degrees of azimuth loss are obtained when one of the rotary magnetic heads reproduces the signal S.sub.VD and the PCM audio signal S.sub.ADNR recorded in respective portions TR.sub.VD and TR.sub.AD of the same slant track. Therefore, the PCM audio signal S.sub.ADNR can be recorded without guard bands between adjacent tracks so long as the two rotary magnetic heads provided for recording and reproducing signals in the adjacent tracks TRA and TRB, respectively, have gaps with different azimuth angles for substantially minimizing cross talk between the PCM audio signals recorded in such adjacent tracks.
Depending upon the application thereof, digital data recorded on a magnetic recording medium may have different sampling frequencies. Therefore, recording media of different types are used for recording digital data having respectively different recording densities. It is apparent that, if a reproducing or playback apparatus can be adapted for reproducing data from the different types of tapes having respectively different recording densities, the uses of such play back apparatus will be accordingly extended. Thus, for example, it is advantageous to provide an 8-mm VTR capable of use with first and second types of recording media, in which the first type of recording medium records PCM audio data having a standard digital information content sampled at a standard sampling frequency, while the second type of recording medium records PCM audio data having a relatively larger content of high-quality digital data sampled at a frequency that is a predetermined multiple of the standard sampling frequency. If these first and second types of recording media can be reproduced in a common 8-mm VTR, that is, the same apparatus can be used for reproducing a standard-quality audio signal from the first type of recording medium and for reproducing a high-quality audio signal from the second type of recording medium, such 8-mm VTR will have a substantially expanded utility.
However, the reproducing apparatus heretofore available has required the user to determine whether the recording medium about to be played back or reproduced is recorded with standard- or high-quality PCM audio or other digital data, and, after making such determination, to select the appropriate processing circuits. Thus, the known reproducing apparatus is relatively inconvenient in that it requires the user thereof to adapt the apparatus for the playback of the type of recording medium in question, and in so doing is susceptible to errors on the part of the user.